Question

The effect of lanthanoid contraction in the lanthanoid series of elements by and large means :

• A. decrease in both atomic and ionic radii
• B. increase in atomic radii and decrease in ionic radii
• C. increase in both atomic and ionic radii
• D. decrease in atomic radii and increase in ionic radii

Answer 1

The Correct Option is A

The lanthanoid contraction refers to the consistent decrease in atomic and ionic radii as one moves across the lanthanoid series from lanthanum (La) to lutetium (Lu). This phenomenon occurs despite the increasing atomic number.

This contraction is primarily due to poor shielding effect provided by the 4f electrons. Let's understand how this causes the decrease:

• Lanthanoids involve filling of 4f orbitals, which are shielded poorly from the nuclear charge.
• As electrons are added to the 4f subshell, the effective nuclear charge experienced by the outer electrons increases.
• This results in a stronger attraction of the electrons towards the nucleus, leading to a decrease in both atomic and ionic radii across the series.

Hence, the correct answer is: decrease in both atomic and ionic radii.

To summarize, the effect of lanthanoid contraction in the lanthanoid series is characterized by a reduction in size, affecting everything from atomic and ionic radii to the chemical behavior of elements in the series. This is a crucial concept in explaining the similarity of chemistry of the heavier post-lanthanide elements.